3Datatypes

This chapter provides a reference to Oracle external datatypes used by OCI applications. It also provides a general discussion of Oracle datatypes, including special datatypes new to Release 8.0. The information in this chapter is useful for understanding the conversions between internal and external representations that occur when you transfer data between your program and Oracle.

Oracle Datatypes

One of the main functions of an OCI program is to communicate with a database through an Oracle server. The OCI application may retrieve data from database tables through SQL SELECT queries, or it may modify existing data in tables through INSERTs, UPDATEs, or DELETEs.

Inside a database, values are stored in columns in tables. Internally, Oracle represents data in particular formats known as internal datatypes. Examples of internal datatypes include NUMBER, CHAR, and DATE.

In general, OCI applications do not work with internal datatype representations of data. OCI applications work with host language datatypes which are predefined by the language in which they are written. When data is transferred between an OCI client application and a database table, the OCI libraries convert the data between internal datatypes and external datatypes.

External datatypes are host language types that have been defined in the OCI header files. When an OCI application binds input variables, one of the bind parameters is an indication of the external datatype code (or SQLT code) of the variable. Similarly, when output variables are specified in a define call, the external representation of the retrieved data must be specified.

In some cases, external datatypes are similar to internal types. External types provide a convenience for the programmer by making it possible to work with host language types instead of proprietary data formats.

Note: Even though some external types are similar to internal types, an OCI application never binds to internal datatypes. They are discussed here because it can be useful to understand how internal types can map to external types.

The OCI is capable of performing a wide range of datatype conversions when transferring data between Oracle and an OCI application. There are more OCI external datatypes than Oracle internal datatypes. In some cases a single external type maps to an internal type; in other cases multiple external types map to an single internal type.

The many-to-one mappings for some datatypes provide flexibility for the OCI programmer.For example, if you are processing the SQL statement

SELECT sal FROM emp WHERE empno = :employee_number

and you want the salary to come back as character data, rather than in a binary floating-point format, specify an Oracle external string datatype, such as VARCHAR2 (code = 1) or CHAR (code = 96) for the dty parameter in the OCIDefineByPos() call for the sal column. You also need to declare a string variable in your program and specify its address in the valuep parameter.

If you want the salary information to be returned as a binary floating-point value, however, specify the FLOAT (code = 4) external datatype. You also need to define a variable of the appropriate type for the valuep parameter.

Oracle performs most data conversions transparently. The ability to specify almost any external datatype provides a lot of power for performing specialized tasks. For example, you can input and output DATE values in pure binary format, with no character conversion involved, by using the DATE external datatype (code = 12). See the description of the DATE external datatype on page 3 - 14 for more information.

To control data conversion, you must use the appropriate external datatype codes in the bind and define routines. You must tell Oracle where the input or output variables are in your OCI program and their datatypes and lengths.

The Oracle8 OCI also supports an additional set of OCI typecodes which are used by Oracle8's type management system to represent datatypes of object type attributes. There is a set of predefined constants which can be used to represent these typecodes. The constants each contain the prefix "OCI_TYPECODE".

In summary, the OCI programmer must be aware of the following different datatypes or data representations:

Internal Datatype Codes

In some circumstances, an OCI application needs to know the internal representation of Oracle data. For example, you many need to know the datatype of a column in a dynamic SQL query so that you can define output variables to received the fetched data. After executing the query, you can use a combination of the OCIParamGet() and OCIAttrGet() functions to obtain describe information about select-list items from the statement handle. You can get the same information from a describe handle without executing the statement by calling OCIDescribeAny(), and then the combination of OCIParamGet() and OCIAttrGet().

Information about a column's internal datatype is conveyed to your application in the form of an internal datatype code. Once your application knows what type of data will be returned, it can make appropriate decisions about how to convert and format the output data. The Oracle internal datatype codes are listed in the section "Internal Datatypes" on page 3-5.

External Datatype Codes

An external datatype code indicates to Oracle how a host variable represents data in your program. This determines how the data is converted when returned to output variables in your program, or how it is converted from input (bind) variables to Oracle column values. For example, if you want to convert a NUMBER in an Oracle column to a variable-length character array, you specify the VARCHAR2 external datatype code in the OCIDefineByPos() call that defines the output variable.

To convert a bind variable to a value in an Oracle column, specify the external datatype code that corresponds to the type of the bind variable. For example, if you want to input a character string such as `02-FEB-65' to a DATE column, specify the datatype as a character string and set the length parameter to nine.

It is always the programmer's responsibility to make sure that values are convertible. If you try to INSERT the string `MY BIRTHDAY' into a DATE column, you will get an error when you execute the statement.

Internal Datatypes

The following table lists the Oracle internal datatypes, along with each type's maximum internal length and datatype code.

Table 3-1 Internal Oracle Datatypes

Internal Oracle Datatype

Maximum Internal Length

Datatype Code

VARCHAR2

4000 bytes

1

NUMBER

21 bytes

2

LONG

2^31-1 bytes

8

ROWID

10 bytes

11

DATE

7 bytes

12

RAW

2000 bytes

23

LONG RAW

2^31-1 bytes

24

CHAR

2000 bytes

96

MLSLABEL

255 bytes

105

User-defined type (object type, VARRAY, Nested Table)

<N/A>

108

REF

<N/A>

111

CLOB

<N/A>

112

BLOB

<N/A>

113

For more information about any of these internal datatypes, see the Oracle8 SQL Reference. The following sections provide OCI-specific information about these datatypes.

LONG, RAW, LONG RAW, VARCHAR2

You can use the piecewise capabilities provided by OCIBindByName(), OCIBindByPos(), OCIDefineByPos(), OCIStmtGetPieceInfo() and OCIStmtSetPieceInfo() to perform inserts, updates or fetches involving column data of these types.

Character Strings and Byte Arrays

You can use five Oracle internal datatypes to specify columns that contain characters or arrays of bytes: CHAR, VARCHAR2, RAW, LONG, and LONG RAW.

Note: LOBs and FILEs may also contain characters or binary data. They are handled differently than other types, so they are not included in this discussion. See the section "LOB and FILE Operations" on page 7-24 for more information about these data types.

CHAR, VARCHAR2, and LONG columns normally hold character data. RAW and LONG RAW hold bytes that are not interpreted as characters, for example, pixel values in a bit-mapped graphics image. Character data can be transformed when passed through a gateway between networks. For example, character data passed between machines using different languages (where single characters may be represented by differing numbers of bytes) can be significantly changed in length. Raw data is never converted in this way.

It is the responsibility of the database designer to choose the appropriate Oracle internal datatype for each column in the table. The OCI programmer must be aware of the many possible ways that character and byte-array data can be represented and converted between variables in the OCI program and Oracle tables.

When an array holds characters, the length parameter for the array in an OCI call is always passed in and returned in bytes, not characters.

External Datatypes

Table 3-2 lists datatype codes for external datatypes. For each datatype, the table lists the program variable types for C from or to which Oracle internal data is normally converted.

Table 3-2 External Datatypes and Codes

EXTERNAL DATATYPE

TYPE OF PROGRAM VARIABLE

OCI DEFINED CONSTANT

NAME

CODE

VARCHAR2

1

char[n]

SQLT_CHR

NUMBER

2

unsigned char[21]

SQLT_NUM

8-bit signed INTEGER

3

signed char

SQLT_INT

16-bit signed INTEGER

3

signed short, signed int

SQLT_INT

32-bit signed INTEGER

3

signed int, signed long

SQLT_INT

FLOAT

4

float, double

SQLT_FLT

Null-terminated STRING

5

char[n+1]

SQLT_STR

VARNUM

6

char[22]

SQLT_VNU

LONG

8

char[n]

SQLT_LNG

VARCHAR

9

char[n+sizeof(short integer)]

SQLT_VCS

ROWID

11

char[n]

SQLT_RID (see note 1)

DATE

12

char[7]

SQLT_DAT

VARRAW

15

unsigned char[n+sizeof(short integer)]

SQLT_VBI

RAW

23

unsigned char[n]

SQLT_BIN

LONG RAW

24

unsigned char[n]

SQLT_LBI

UNSIGNED INT

68

unsigned

SQLT_UIN

LONG VARCHAR

94

char[n+sizeof(integer)]

SQLT_LVC

LONG VARRAW

95

unsigned char[n+sizeof(integer)]

SQLT_LVB

CHAR

96

char[n]

SQLT_AFC

CHARZ

97

char[n+1]

SQLT_AVC

ROWID descriptor

104

OCIRowid

SQLT_RDD

MLSLABEL

106

char[n]

SQLT_LAB

NAMED DATA TYPE

108

struct

SQLT_NTY

REF

110

OCIRef

SQLT_REF

Character LOB

112

OCILobLocator (see note 3)

SQLT_CLOB

Binary LOB

113

OCILobLocator (see note 3)

SQLT_BLOB

Binary FILE

114

OCILobLocator

SQLT_FILE

OCI string type

155

OCIString

SQLT_VST (see note 2)

OCI date type

156

OCIDate

SQLT_ODT (see note 2)

Notes:

(1) This type is valid only for version 7.x OCI calls. Oracle8 OCI applications should use the ROWID descriptor (type 104).

The following three types are internal to PL/SQL and cannot be returned as values by OCI:

Boolean, SQLT_BOL

Indexed Table, SQLT_TAB

Record, SQLT_REC

VARCHAR2

The VARCHAR2 datatype is a variable-length string of characters with a maximum length of 4000 bytes.

Note: If you are using Oracle8 objects, you can work with a special OCIString external datatype using a set of predefined OCI functions. Refer to Chapter 9, "Object-Relational Datatypes" for more information about this datatype.

Input

The value_sz parameter determines the length in the OCIBindByName() or OCIBindByPos() call.

If the value_sz parameter is greater than zero, Oracle obtains the bind variable value by reading exactly that many bytes, starting at the buffer address in your program. Trailing blanks are stripped, and the resulting value is used in the SQL statement or PL/SQL block. If, in the case of an INSERT statement, the resulting value is longer than the defined length of the database column, the INSERT fails, and an error is returned.

Note: A trailing null is not stripped. Variables should be blank-padded but not null-terminated.

If the value_sz parameter is zero, Oracle treats the bind variable as a null, regardless of its actual content. Of course, a null must be allowed for the bind variable value in the SQL statement. If you try to insert a null into a column that has a NOT NULL integrity constraint, Oracle issues an error, and the row is not inserted.

When the Oracle internal (column) datatype is NUMBER, input from a character string that contains the character representation of a number is legal. Input character strings are converted to internal numeric format. If the VARCHAR2 string contains an illegal conversion character, Oracle returns an error and the value is not inserted into the database.

Output

Specify the desired length for the return value in the value_sz parameter of the OCIDefineByPos() call, or the value_sz parameter of OCIBindByName() or OCIBindByPos() for PL/SQL blocks. If zero is specified for the length, no data is returned.

If you omit the rlenp parameter of OCIDefineByPos(), returned values are blank-padded to the buffer length, and nulls are returned as a string of blank characters. If rlenp is included, returned values are not blank-padded. Instead, their actual lengths are returned in the rlenp parameter.

To check if a null is returned or if character truncation has occurred, include an indicator parameter in the OCIDefineByPos() call. Oracle sets the indicator parameter to -1 when a null is fetched and to the original column length when the returned value is truncated. Otherwise, it is set to zero. If you do not specify an indicator parameter and a null is selected, the fetch call returns the error code OCI_SUCCESS_WITH_INFO. Retrieving diagnostic information on the error will return ORA-1405.

You can also request output to a character string from an internal NUMBER datatype. Number conversion follows the conventions established by National Language Support for your system. For example, your system might be configured to recognize a comma rather than period as the decimal point.

NUMBER

You should not need to use NUMBER as an external datatype. If you do use it, Oracle returns numeric values in its internal 21-byte binary format and will expect this format on input. The following discussion is included for completeness only.

Note: If you are using objects in Oracle8, you can work with a special OCINumber datatype using a set of predefined OCI functions. Refer to Chapter 9, "Object-Relational Datatypes" for more information about this datatype.

Oracle stores values of the NUMBER datatype in a variable-length format. The first byte is the exponent and is followed by 1 to 20 mantissa bytes. The high-order bit of the exponent byte is the sign bit; it is set for positive numbers. The lower 7 bits represent the exponent, which is a base-100 digit with an offset of 65.

Each mantissa byte is a base-100 digit, in the range 1..100. For positive numbers, the digit has 1 added to it. So, the mantissa digit for the value 5 is 6. For negative numbers, instead of adding 1, the digit is subtracted from 101. So, the mantissa digit for the number -5 is 96 (101-5). Negative numbers have a byte containing 102 appended to the data bytes. However, negative numbers that have 20 mantissa bytes do not have the trailing 102 byte. Because the mantissa digits are stored in base 100, each byte can represent 2 decimal digits. The mantissa is normalized; leading zeroes are not stored.

Up to 20 data bytes can represent the mantissa. However, only 19 are guaranteed to be accurate. The 19 data bytes, each representing a base-100 digit, yield a maximum precision of 38 digits for an Oracle NUMBER.

If you specify the datatype code 2 in the dty parameter of an OCIDefineByPos() call, your program receives numeric data in this Oracle internal format. The output variable should be a 21-byte array to accommodate the largest possible number. Note that only the bytes that represent the number are returned. There is no blank padding or null termination. If you need to know the number of bytes returned, use the VARNUM external datatype instead of NUMBER. See the description of VARNUM on for examples of the Oracle internal number format.

INTEGER

The INTEGER datatype converts numbers. An external integer is a signed binary number; the size in bytes is system dependent. The host system architecture determines the order of the bytes in the variable. A length specification is required for input and output. If the number being returned from Oracle is not an integer, the fractional part is discarded, and no error or other indication is returned. If the number to be returned exceeds the capacity of a signed integer for the system, Oracle returns an "overflow on conversion" error.

FLOAT

The FLOAT datatype processes numbers that have fractional parts or that exceed the capacity of an integer. The number is represented in the host system's floating-point format. Normally the length is either four or eight bytes. The length specification is required for both input and output.

The internal format of an Oracle number is decimal, and most floating-point implementations are binary; therefore Oracle can represent numbers with greater precision than floating-point representations.

Note: You may receive a round-off error when converting between FLOAT and NUMBER. Thus, using a FLOAT as a bind variable in a query may return an ORA-1403 error. You can avoid this situation by converting the FLOAT into a STRING and then using datatype code 1 or 5 for the operation.

STRING

The null-terminated STRING format behaves like the VARCHAR2 format (datatype code 1), except that the string must contain a null terminator character. This datatype is most useful for C programs.

Input

The string length supplied in the OCIBindByName() or OCIBindByPos() call limits the scan for the null terminator. If the null terminator is not found within the length specified, Oracle issues the error

ORA-01480: trailing null missing from STR bind value

If the length is not specified in the bind call, the OCI uses an implied maximum string length of 4000.

The minimum string length is two bytes. If the first character is a null terminator and the length is specified as two, a null is inserted in the column, if permitted. Unlike types 1 and 96, a string containing all blanks is not treated as a null on input; it is inserted as is.

Note: Unlike earlier versions of the OCI, in release 8.0 you cannot pass -1 for the string length parameter of a null-terminated string.

Output

A null terminator is placed after the last character returned. If the string exceeds the field length specified, it is truncated and the last character position of the output variable contains the null terminator.

A null select-list item returns a null terminator character in the first character position. An ORA-01405 error is possible, as well.

VARNUM

The VARNUM datatype is like the external NUMBER datatype, except that the first byte contains the length of the number representation. This length does not include the length byte itself. Reserve 22 bytes to receive the longest possible VARNUM. Set the length byte when you send a VARNUM value to Oracle.

Table 3 - 3 shows several examples of the VARNUM values returned for numbers in an Oracle table.

Table 3-3 VARNUM Examples

Decimal Value

Length Byte

Exponent Byte

Mantissa Bytes

Terminator Byte

0

1

128

n/a

n/a

5

2

193

6

n/a

-5

3

62

96

102

2767

3

194

28, 68

n/a

-2767

4

61

74, 34

102

100000

2

195

11

n/a

1234567

5

196

2, 24, 46, 68

n/a

LONG

The LONG datatype stores character strings longer than 4000 bytes. You can store up to two gigabytes (2^31-1 bytes) in a LONG column. Columns of this type are used only for storage and retrieval of long strings. They cannot be used in functions, expressions, or WHERE clauses. LONG column values are generally converted to and from character strings.

VARCHAR

The VARCHAR datatype stores character strings of varying length. The first two bytes contain the length of the character string, and the remaining bytes contain the string. The specified length of the string in a bind or a define call must include the two length bytes, so the largest VARCHAR string that can be received or sent is 65533 bytes long, not 65535. For converting longer strings, use the LONG VARCHAR external datatype.

ROWID

The ROWID datatype identifies a particular row in a database table. ROWID can be a select-list item in a query; for example:

SELECT rowid, ename, sal FROM emp FOR UPDATE OF sal

In this case, you use the returned ROWID in further INSERT, UPDATE, or DELETE statements. This can be the fastest way to access a particular row.

DATE

The DATE datatype can update, insert, or retrieve a date value using the Oracle internal date binary format. A date in binary format contains seven bytes, as shown in Table 3-4.

Table 3-4 Format of the DATE Datatype

Byte

1

2

3

4

5

6

7

Meaning

Century

Year

Month

Day

Hour

Minute

Second

Example(for 30-NOV-1992, 3:17 PM)

119

192

11

30

16

18

1

The century and year bytes are in an excess-100 notation. Dates Before Common Era (BCE) are less than 100. The era begins on 01-JAN-4712 BCE, which is Julian day 1. For this date, the century byte is 53, and the year byte is 88. The hour, minute, and second bytes are in excess-1 notation. The hour byte ranges from 1 to 24, the minute and second bytes from 1 to 60. If no time was specified when the date was created, the time defaults to midnight (1, 1, 1).

When you enter a date in binary format using the DATE external datatype, the database does not do consistency or range checking. All data in this format must be carefully validated before input.

Note: There is little need to use the Oracle external DATE datatype in ordinary database operations. It is much more convenient to convert DATEs into character format, because the program usually deals with data in a character format, such as `DD-MON-YY'.

When a DATE column is converted to a character string in your program, it is returned using the default format mask for your session, or as specified in the INIT.ORA file.

Note: If you are using objects in Oracle8, you can work with a special OCIDate datatype using a set of predefined OCI functions. Refer to Chapter 9, "Object-Relational Datatypes" for more information about this datatype.

RAW

The RAW datatype is used for binary data or byte strings that are not to be interpreted by Oracle, for example, to store graphics character sequences. The maximum length of a RAW column is 2000 bytes. For more information, see theOracle8 SQL Reference.

When RAW data in an Oracle table is converted to a character string in a program, the data is represented in hexadecimal character code. Each byte of the RAW data is returned as two characters that indicate the value of the byte, from '00' to 'FF'. If you want to input a character string in your program to a RAW column in an Oracle table, you must code the data in the character string using this hexadecimal code.

You can use the piecewise capabilities provided by OCIDefineByPos(), OCIBindByName(), OCIBindByPos(), OCIStmtGetPieceInfo(), and OCIStmtSetPieceInfo() to perform inserts, updates, or fetches involving RAW (or LONG RAW) columns.

Note: If you are using objects in Oracle8, you can work with a special OCIRaw datatype using a set of predefined OCI functions. Refer to Chapter 9, "Object-Relational Datatypes" for more information about this datatype.

VARRAW

The VARRAW datatype is similar to the RAW datatype. However, the first two bytes contain the length of the data. The specified length of the string in a bind or a define call must include the two length bytes. So the largest VARRAW string that can be received or sent is 65533 bytes long, not 65535. For converting longer strings, use the LONG VARRAW external datatype.

LONG RAW

The LONG RAW datatype is similar to the RAW datatype, except that it stores raw data with a length up to two gigabytes (2^31-1 bytes).

UNSIGNED

The UNSIGNED datatype is used for unsigned binary integers. The size in bytes is system dependent. The host system architecture determines the order of the bytes in a word. A length specification is required for input and output. If the number being output from Oracle is not an integer, the fractional part is discarded, and no error or other indication is returned. If the number to be returned exceeds the capacity of an unsigned integer for the system, Oracle returns an "overflow on conversion" error.

LONG VARCHAR

The LONG VARCHAR datatype stores data from and into an Oracle LONG column. The first four bytes of a LONG VARCHAR contain the length of the item. So, the maximum length of a stored item is 2^31-5 bytes.

LONG VARRAW

The LONG VARRAW datatype is used to store data from and into an Oracle LONG RAW column. The length is contained in the first four bytes. The maximum length is 2^31-5 bytes.

CHAR

The CHAR datatype is a string of characters, with a maximum length of 2000. CHAR strings are compared using blank-padded comparison semantics (see the Oracle8 SQL Reference).

Input

The length is determined by the value_sz parameter in the OCIBindByName() or OCIBindByPos() call.

Note: The entire contents of the buffer (value_sz chars) is passed to the database, including any trailing blanks or nulls.

If the value_sz parameter is zero, Oracle treats the bind variable as a null, regardless of its actual content. Of course, a null must be allowed for the bind variable value in the SQL statement. If you try to insert a null into a column that has a NOT NULL integrity constraint, Oracle issues an error and does not insert the row.

Negative values for the value_sz parameter are not allowed for CHARs.

When the Oracle internal (column) datatype is NUMBER, input from a character string that contains the character representation of a number is legal. Input character strings are converted to internal numeric format. If the CHAR string contains an illegal conversion character, Oracle returns an error and does not insert the value. Number conversion follows the conventions established by National Language Support settings for your system. For example, your system might be configured to recognize a comma (,) rather than a period (.) as the decimal point.

Output

Specify the desired length for the return value in the value_sz parameter of the OCIDefineByPos() call. If zero is specified for the length, no data is returned.

If you omit the rlenp parameter of OCIDefineByPos(), returned values are blank padded to the buffer length, and nulls are returned as a string of blank characters. If rlenp is included, returned values are not blank padded. Instead, their actual lengths are returned in the rlenp parameter.

To check whether a null is returned or if character truncation has occurred, include an indicator parameter or array of indicator parameters in the OCIDefineByPos() call. An indicator parameter is set to -1 when a null is fetched and to the original column length when the returned value is truncated. Otherwise, it is set to zero. If you do not specify an indicator parameter and a null is selected, the fetch call returns an ORA-01405 error.

You can also request output to a character string from an internal NUMBER datatype. Number conversion follows the conventions established by the National Language Support settings for your system. For example, your system might use a comma (,) rather than a period (.) as the decimal point.

CHARZ

The CHARZ external datatype is similar to the CHAR datatype, except that the string must be null terminated on input, and Oracle places a null-terminator character at the end of the string on output. The null terminator serves only to delimit the string on input or output; it is not part of the data in the table.

On input, the length parameter must indicate the exact length, including the null terminator. For example, if an array in C is declared as

char my_num[] = "123.45";

then the length parameter when you bind my_num must be seven. Any other value would return an error for this example.

You can define a column using the MLSLABEL datatype in Oracle8 for compatibility with Trusted Oracle applications, but the only valid value for the column in Oracle8 is NULL.

See the Trusted Oracle Server Administrator's Guide for more information about the MLSLABEL datatype and Trusted Oracle.

New OCI 8.0 External Datatypes

The following new external datatypes are being introduced with release 8.0. These datatypes are not supported when connect to an Oracle7 server.

Note: Both internal and external datatypes have Oracle-defined constant values (e.g., SQLT_NTY, SQLT_REF) corresponding to their datatype codes. Although the constants are not listed for all of the types in this chapter, they are used in this section when discussing new Oracle8 datatypes. The datatype constants are also used in other chapters of this guide when referring to these new types.

Note: Named data types and REFs are only available if you have purchased the Oracle8 Enterprise Edition.

NAMED DATA TYPE

Named data types are user-defined types which are specified with the CREATE TYPE command in SQL. Examples include object types, varrays, and nested tables. In the OCI, "named data type" refers to a host language representation of the type. The SQLT_NTY datatype code is used when binding or defining named data types.

In a C application, named data types are represented as C structs. These structs can be generated from types stored in the database by using the Object Type Translator. These types correspond to OCI_TYPECODE_OBJECT.

See Also: For more information about working with named data types in the OCI, refer to Part 2 of this guide.

REF

This is a reference to a named data type. The C language representation of a REF is a variable declared to be of type OCIRef *. The SQLT_REF datatype code is used when binding or defining REFs.

Access to REFs is only possible when an OCI application has been initialized in object mode. When REFs are retrieved from the server, they are stored in the client-side object cache.

To allocate a REF for use in your application, you should declare a variable to be a pointer to a REF, and then call OCIObjectNew(), passing OCI_TYPECODE_REF as the typecode parameter.

See Also: For more information about working with REFs in the OCI, refer to Part 2 of this guide.

LOB

A LOB (Large OBject) stores binary or character data up to 4 gigabytes in length. Binary data is stored in a BLOB (Binary LOB), and character data is stored in a CLOB (Character LOB) or NCLOB (National Character LOB).

LOB values may or may not be stored inline with other row data in the database. In either case, LOBs have the full transactional support of the database server. A database table stores a LOB locator which points to the LOB value which may be in a different storage space.

When an OCI application issues a SQL query which includes a LOB column or attribute in its select-list, fetching the result(s) of the query returns the locator, rather than the actual LOB value. In the OCI, the LOB locator maps to a variable of type OCILobLocator.

To write into or read from an NCLOB, the user must set the character set form (csfrm) parameter to be SQLCS_NCHAR.

The "amount" (amtp) parameter in calls involving CLOBS and NCLOBS is always interpreted in terms of characters, rather than bytes.

FILE

The FILE datatype provides access to file LOBs that are stored in file systems outside the Oracle8 database. Oracle8 currently supports access to binary files, or BFILEs.

A BFILE column or attribute stores a file LOB locator, which serves as a pointer to a binary file on the server's file system. The locator maintains the directory alias and the filename.

Binary file LOBs do not participate in transactions. Rather, the underlying operating system provides file integrity and durability. The maximum file size supported is 4 gigabytes.

The database administrator must ensure that the file exists and that Oracle8 processes have operating system read permissions on the file.

The BFILE datatype allows read-only support of large binary files; you cannot modify a file through Oracle. Oracle8 provides APIs to access file data. The primary interfaces that you use to access file data are the PL/SQL DBMS_LOB package, and the OCI.

BLOB

The BLOB datatype stores unstructured binary large objects. BLOBs can be thought of as bitstreams with no character set semantics. BLOBs can store up to four gigabytes of binary data.

BLOBs have full transactional support; changes made through the PL/SQL DBMS_LOB package, or the OCI participate fully in the transaction. The BLOB value manipulations can be committed or rolled back. You cannot save a BLOB locator in a PL/SQL or OCI variable in one transaction and then use it in another transaction or session.

CLOB

The CLOB datatype stores single-byte character data. Varying-width character sets are not supported. CLOBs can store up to 4 gigabytes of character data.

CLOBs have full transactional support; changes made through the PL/SQL DBMS_LOB package or the OCI participate fully in the transaction. The CLOB value manipulations can be committed or rolled back. You cannot save a CLOB locator in a PL/SQL or OCI variable in one transaction and then use it in another transaction or session.

NCLOB

An NCLOB is a national character version of a CLOB. It stores fixed-width, single- or multi-byte national character set character (NCHAR) data. Varying-width character sets are not supported. NCLOBs can store up to 4 gigabytes of character text data.

NCLOBs have full transactional support; changes made through the PL/SQL DBMS_LOB package, or the OCI participate fully in the transaction. NCLOB value manipulations can be committed or rolled back. You cannot save a NCLOB locator in a PL/SQL or OCI variable in one transaction and then use it in another transaction or session.

You cannot create an object with NCLOB attributes, but you can specify NCLOB parameters in methods.

New C Datatype Mappings

The OCI now includes support for Oracle-defined C datatypes used to map user-defined datatypes and ADT attributes to C representations (e.g. OCINumber, OCIArray). The OCI provides a set of calls to operate on these datatypes, and to use these datatypes in bind and define operations, in conjunction with OCI external datatype codes. For information on using these Oracle-defined C datatypes, refer to Chapter 9, "Object-Relational Datatypes".

Data Conversions

Table 3-5 shows the supported conversions from internal Oracle datatypes to external datatypes, and from external datatypes into internal column representations, for all datatypes available through release 7.3. Information about data conversions for data types new to release 8.0 is listed here:

REFs stored in the database are converted to SQLT_REF on output.

SQLT_REF is converted to the internal representation of REFs on input.

Named Data Types stored in the database can be converted to SQLT_NTY (and represented by a C struct in the application) on output.

SQLT_NTY (represented by a C struct in an application) is converted to the internal representation of the corresponding type on input.

LOBs and BFILEs are represented by descriptors in OCI applications, so there are no input or output conversions.

(1) For input, host string must be in Oracle ROWID format. On output, column value is returned in Oracle ROWID format.

(2) For input, host string must be in the Oracle DATE character format. On output, column value is returned in Oracle DATE format.

(3) For input, host string must be in hex format. On output, column value is returned in hex format.

(4) For output, column value must represent a valid number.

(5) Length must be less than or equal to 2000.

(6) On input, column value is stored in hex format. On output, column value must be in hex format.

(7) For input, host string must be a valid OS label in text format. On output, column value is returned in OS label text format.

(8) For character representation of MLSLABEL, use the TO_CHAR(mlscolumn) function.

Legend:

I = Conversion valid for input only

O = Conversion valid for output only

I/O = Conversion valid for input or output

Typecodes

There is a unique typecode associated with each Oracle8 type, whether scalar, collection, reference, or object type. This typecode identifies the type, and is used by Oracle to manage information about object type attributes. This typecode system is designed to be generic and extensible, and is not tied to a direct one-to-one mapping to Oracle datatypes. Consider the following SQL statements:

These statements create an object type and an object table. When it is created, my_table will have three columns, all of which are of Oracle NUMBER type, because SMALLINT and INTEGER map internally to NUMBER. The internal representation of the attributes of my_type, however, maintains the distinction between the datatypes of the three attributes: attr1 is OCI_TYPECODE_NUMBER, attr2 is OCI_TYPECODE_INTEGER, and attr3 is OCI_TYPECODE_SMALLINT. If an application describes my_type, these typecodes are returned.

OCITypeCode is the C datatype of the typecode. The typecode is used by some OCI functions, like OCIObjectNew() (where it helps determine what type of object is created). It is also returned as the value of some attributes when an object is described; e.g., querying the OCI_ATTR_TYPECODE attribute of a type returns an OCITypeCode value.

Table 3-6 lists the possible values for an OCITypeCode. There is a value corresponding to each Oracle8 datatype.

Table 3-6 OCITypeCode Values

Value

Datatype

OCI_TYPECODE_REF

REF

OCI_TYPECODE_DATE

date

OCI_TYPECODE_REAL

single-precision real

OCI_TYPECODE_DOUBLE

double-precision real

OCI_TYPECODE_FLOAT

floating-point

OCI_TYPECODE_NUMBER

Oracle number

OCI_TYPECODE_DECIMAL

decimal

OCI_TYPECODE_OCTET

octet

OCI_TYPECODE_INTEGER

integer

OCI_TYPECODE_SMALLINT

smallint

OCI_TYPECODE_RAW

RAW

OCI_TYPECODE_VARCHAR2

variable string ANSI SQL, i.e., VARCHAR2

OCI_TYPECODE_VARCHAR

variable string Oracle SQL, i.e., VARCHAR

OCI_TYPECODE_CHAR

fixed-length string inside SQL, i.e. SQL CHAR

OCI_TYPECODE_VARRAY

variable-length array (varray)

OCI_TYPECODE_TABLE

multiset

OCI_TYPECODE_CLOB

character large object (CLOB)

OCI_TYPECODE_BLOB

binary large object (BLOB)

OCI_TYPECODE_BFILE

binary large object file (BFILE)

OCI_TYPECODE_OBJECT

named object type

OCI_TYPECODE_NAMEDCOLLECTION

Domain (named primitive type)

Relationship Between SQLT and OCI_TYPECODE Values

Oracle recognizes two different sets of datatype code values. One set is distinguished by the "SQLT_" prefix, the other by the "OCI_TYPECODE_" prefix.

The SQLT typecodes are used by OCI to specify a datatype in a bind or define operation. In this way, the SQL typecodes help to control data conversions between Oracle and OCI client applications. The OCI_TYPECODE types are used by Oracle8's type system to reference or describe predefined types when manipulating or creating user-defined types.

In many cases there are direct mappings between SQLT and OCI_TYPECODE values. In other cases, however, there is not a direct one-to-one mapping. For example OCI_TYPECODE_SIGNED16, OCI_TYPECODE_SIGNED32, OCI_TYPECODE_INTEGER, OCI_TYPECODE_OCTET, and OCI_TYPECODE_SMALLINT are all mapped to the SQLT_INT type.

The following table illustrates the mappings between SQLT and OCI_TYPECODE types.

Table 3-7 OCI_TYPECODE to SQLT Mappings

Oracle Type System Typename

Oracle Type System Type

Equivalent SQLT Type

BFILE

OCI_TYPECODE_BFILE

SQLT_BFILE

BLOB

OCI_TYPECODE_BLOB

SQLT_BLOB

CHAR

OCI_TYPECODE_CHAR (n)

SQLT_AFC(n) [note 1]

CLOB

OCI_TYPECODE_CLOB

SQLT_CLOB

COLLECTION

OCI_TYPECODE_NAMEDCOLLECTION

SQLT_NCO

DATE

OCI_TYPECODE_DATE

SQLT_DAT

FLOAT

OCI_TYPECODE_FLOAT (b)

SQLT_FLT (8) [note 2]

DECIMAL

OCI_TYPECODE_DECIMAL (p)

SQLT_NUM (p, 0) [note 3]

DOUBLE

OCI_TYPECODE_DOUBLE

SQLT_FLT (8)

INTEGER

OCI_TYPECODE_INTEGER

SQLT_INT (i) [note 4]

NUMBER

OCI_TYPECODE_NUMBER (p, s)

SQLT_NUM (p, s) [note 5]

OCTECT

OCI_TYPECODE_OCTECT

SQLT_INT (1)

POINTER

OCI_TYPECODE_PTR

<NONE>

RAW

OCI_TYPECODE_RAW

SQLT_LVB

REAL

OCI_TYPECODE_REAL

SQLT_FLT (4)

REF

OCI_TYPECODE_REF

SQLT_REF

OBJECT

OCI_TYPECODE_OBJECT

SQLT_NTY

SIGNED(8)

OCI_TYPECODE_SIGNED8

SQLT_INT (1)

SIGNED(16)

OCI_TYPECODE_SIGNED16

SQLT_INT (2)

SIGNED(32)

OCI_TYPECODE_SIGNED32

SQLT_INT (4)

SMALLINT

OCI_TYPECODE_SMALLINT

SQLT_INT (i) [note 4]

TABLE [note 6]

OCI_TYPECODE_TABLE

SQLT_TAB

UNSIGNED(8)

OCI_TYPECODE_UNSIGNED8

SQLT_UIN (1)

UNSIGNED(16)

OCI_TYPECODE_UNSIGNED16

SQLT_UIN (2)

UNSIGNED(32)

OCI_TYPECODE_UNSIGNED32

SQLT_UIN (4)

VARRAY [note 6]

OCI_TYPECODE_VARRAY

SQLT_NAR

VARCHAR

OCI_TYPECODE_VARCHAR (n)

SQLT_CHR (n) [note 1]

VARCHAR2

OCI_TYPECODE_VARCHAR2 (n)

SQLT_VCS (n) [note 1]

Notes:

1. n is the size of the string in bytes

2. These are floating point numbers, the precision is given in terms of binary digits. b is the precision of the number in binary digits.

3. This is equivalent to a NUMBER with no decimal places.

4. i is the size of the number in bytes, set as part of an OCI call.

5. p is the precision of the number in decimal digits; s is the scale of the number in decimal digits.

6. Can only be part of a named collection type.

Definitions in oratypes.h

Throughout this guide you will see references to datatypes like ub2 or sb4, or to constants like UB4MAXVAL. These types are defined in the oratypes.h header file, an example of which is included here. The exact contents may vary according to the platform you are using.